In mineral ore flotation, depression comprises steps taken to prevent the flotation of a particular mineral. In one-mineral flotation systems, it is commonly practiced to hold down both the gangue materials and low-assay middlings. In differential flotation systems, it is used to hold back one or more of the materials normally flotable by a given collector.
Depression is conventionally accomplished through the use of reagents known as depressing agents or, more commonly, depressants. When added to the flotation systems, the depressing agents exert a specific action upon the material to be depressed thereby preventing that material from floating. The exact mode of this action remains open to speculation. Various theories have been put forth to explain this action; some of which include: that the depressants react chemically with the mineral surface to produce insoluble protective films of a wettable nature which fail to react with collectors; That the depressants, by various physical-chemical mechanisms, such as surface absorption, mass-action effects, complex formation, or the like, prevent the formation of the collector film; that the depressants act as solvents for an activating film naturally associated with the mineral; that the depressants act as solvents for the collecting film; and the like. These theories appear closely related and the correct theory may ultimately prove to involve elements from several, if not all, of them.
Currently, nonsulfide flotation systems such as iron oxide utilize depressants derived from natural substances such as water soluble starches, dextrins, guar gums and the like. See U.S. Pat. No. 3,292,780 to Frommer et al. and U.S. Pat. No. 3,371,778 to Iwasaki. However, from an ecological vantage point, the presence of residual depressants such as these in the waste waters increase the biodegradeable oxygen demand and the chemical oxygen demand, thereby creating a pollution problem in the disposal of these waste waters. From a commercial vantage point, there is an ever-increasing number of countries in which use of reagents having a food value, such as starch, is prohibited in commercial applications. Furthermore, the starch-type depressants require a complex preparation of the reagent solution involving a cooling stage prior to solution and the resultant reagent is susceptible to bacterial decomposition thereby requiring storage monitoring.
In other nonsulfide mineral ore flotation processes, such as sylvinite ore, the gangue clay is depressed whereas the valuable sylvite is floated with the aid of amine collectors. Various depressants, also referred to as blinding agents, used in these flotation systems have been described in U.S. Pat. Nos. 3,452,867 to Bishop; 3,782,546 to Kirwin; 3,805,951 to Brogoitti 3,456,790 to Fast; 2,288,497 and 2,364,520; and in German Offen 1,267,631 to Budan and Canadian Pat. No. 932,485 to Fee. Various other nonsulfide mineral ore depressants have been described in U.S. Pat. Nos. 3,572,504 to DeCuyper; 2,740,552 to Aimone and 3,929,629 to Griffith as well as in U.S.S.R. Pat. Nos. 130.428 to Gurvich and 141.826 to Livhits. In all of the aforementioned references the depressants disclosed are distinct in chemical structure and many properties than those employed in the instant process.
Accordingly, there exists the need for a synthetic depressant which can at once overcome the drawbacks of the conventional depressants currently utilized and yet perform in an equivalent or superior manner.